Brakes work at first?

Question

When I first start driving they are a little soft. Then after a few minutes they lock up and it won"t move.

Answer 1

If it is the rear brakes they are adjusted too tight. and are locking up when they get hot and expand. Self adjuster normally work when stopping in reverse. So if you do a lot of backing in and out of parking places they might adjusted out too tight. Had that happen to me once on wife's car. Didn't allow for her driving habits. Brakes locked up on her at mall. Got me a lot of purse knots on my head.
As far as feeling soft and mushy that sounds like your master cylinder since you didn';t say anything about car pulling right or left when stopping.
Worn brake pads and brake shoes can also cause that. If they are worn too much it can also cause the master cylinder not to return all the back and your brakes in that case will drag over heating them and making the lock up. When that happens it is usually a combination of worn brakes and master cylinder going out. Seen that a couple of times. It doesn't happen much but it does happen.
Something else that can cause that is if your equalizer block is hanging and not allowing the brakes to release fully. I guess the best way to explain that is, the equalizer block is sort of the early mechanic version of abs. What it does is equalize your braking between you front and rear brakes so your braking will be balanced out between front and rear. This is especially true when you have a mixed brake system "rear drum brakes and front disc brakes.
I have also seen that when after doing a brake job and the mechanics used rebuilt master cylinders instead of new ones. For that reason I do not like rebuilt Master cylinders or calipers. When I do brake job I use new Master cylinders and calipers. If customers don't want to pay the extra money for new ones I don't do the job. And I use factory original parts not after market parts. If it is a Ford I use Motorcraft, a GM car or truck I use Delco, a Chrysler product. Mopar.

Answer 2

For some reason it's building up pressure and holding the brakes on. Call a tow company, explain that the brakes lock up so they can make sure they have dollies or a flat bed, and tow it in to your mechanic to be fixed. Bet you also have a brake light warning lit up on the dash.

Answer 3

check the master cylinder for brake fluid or maybe a sticky caliper

Answer 4

sounds like a master cylinder. have a shop give you a better diagnosis.